Scientists unlock secrets of a sixth basic flavour; in addition to sweet, sour, salty and bitter

TOKY: Japanese scientist Kikunae Ikeda first proposed umami as a basic taste—in addition to sweet, sour, salty and bitter—in the early 1900s. About eight decades later, the scientific community officially agreed with him. Now, scientists led by researchers at the USC Dornsife College of Letters, Arts and Sciences have evidence of a sixth basic taste.

In research published in Nature Communications, USC Dornsife neuroscientist Emily Liman and her team found that the tongue responds to ammonium chloride through the same protein receptor that signals sour taste.

“If you live in a Scandinavian country, you will be familiar with and may like this taste,” says Liman, professor of biological sciences. In some northern European countries, salt licorice has been a popular candy at least since the early 20th century. The treat counts among its ingredients salmiak salt, or ammonium chloride.

Scientists have for decades recognized that the tongue responds strongly to ammonium chloride. However, despite extensive research, the specific tongue receptors that react to it remained elusive.

Liman and the research team thought they might have an answer.

In recent years, they uncovered the protein responsible for detecting sour taste. That protein, called OTOP1, sits within cell membranes and forms a channel for hydrogen ions moving into the cell.

Hydrogen ions are the key component of acids, and as foodies everywhere know, the tongue senses acid as sour. That’s why lemonade (rich in citric and ascorbic acids), vinegar (acetic acid) and other acidic foods impart a zing of tartness when they hit the tongue. Hydrogen ions from these acidic substances move into taste receptor cells through the OTOP1 channel.

Because ammonium chloride can affect the concentration of acid—that is, hydrogen ions—within a cell, the team wondered if it could somehow trigger OTOP1.

To answer this question, they introduced the Otop1 gene into lab-grown human cells so the cells produce the OTOP1 receptor protein. They then exposed the cells to acid or to ammonium chloride and measured the responses.

“We saw that ammonium chloride is a really strong activator of the OTOP1 channel,” Liman said. “It activates as well or better than acids.”

Ammonium chloride gives off small amounts of ammonia, which moves inside the cell and raises the pH, making it more alkaline, which means fewer hydrogen ions.

“This pH difference drives a proton influx through the OTOP1 channel,” explained Ziyu Liang, a Ph.D. student in Liman’s lab and first author on the study.

To confirm that their result was more than a laboratory artifact, they turned to a technique that measures electrical conductivity, simulating how nerves conduct a signal. Using taste bud cells from normal mice and from mice the lab previously genetically engineered to not produce OTOP1, they measured how well the taste cells generated electrical responses called action potentials when ammonium chloride is introduced. (IANS)

Also Read: Scientists hint at existence of closest black holes to Earth

Also Watch: